Search results for "Reverse"
showing 10 items of 1361 documents
Selective downregulation of the MDR1 gene product in Caco-2 cells by stable transfection to prove its relevance in secretory drug transport.
2005
Considerable interest is focused on overcoming multidrug resistance (MDR) in cancer chemotherapy. The in vitro experiments to characterize P-glycoprotein's (P-gp) function and to decrease its effects have led to a variety of strategies such as addition of competitors or supplementation of the medium with oligonucleotides complementary to the 5'-end of the MDR1-mRNA. For the Caco-2 cell line, an in vitro model for absorption screening, expressing multiple transporters including P-gp, which pumps substances back into the apical solution, P-gp activity might mask other relevant transport proteins' activity. The objective of the present study was to construct a Caco-2 subline with reduced P-gp …
Effect of short-chain alcohols on surfactant-mediated reversed-phase liquid chromatographic systems.
2010
The behaviour of β-blockers in a reversed-phase liquid chromatographic (RPLC) column with mobile phases containing a short-chain alcohol (methanol, ethanol or 1-propanol), with and without the surfactant sodium dodecyl sulphate (SDS), was explored. Two surfactant-mediated RPLC modes were studied, where the mobile phases contained either micelles or only surfactant monomers at high concentration. Acetonitrile was also considered for comparison purposes. A correlation was found between the effects of the organic solvent on micelle formation (monitored by the drop weight procedure) and on the nature of the chromatographic system (as revealed by the retention, elution strength and peak shape of…
Submicellar and micellar reversed-phase liquid chromatographic modes applied to the separation of beta-blockers.
2009
The behaviour of a reversed-phase liquid chromatographic (RPLC) system (i.e. elution order, resolution and analysis time), used in the analysis of β-blockers with acetonitrile-water mobile phases, changes drastically upon addition of an anionic surfactant (sodium dodecyl sulphate, SDS). Surfactant monomers cover the alkyl-bonded phase in different extent depending on the concentration of both modifiers, in the ranges 1 × 10-3-0.15 M SDS and 5-50% acetonitrile. Meanwhile, the surfactant is dissolved in the mobile phase as free monomers, associated in small clusters or forming micelles. Four characteristic RPLC modes are yielded, with transition regions between them: hydro-organic, micellar, …
Performance of different C18 columns in reversed-phase liquid chromatography with hydro-organic and micellar-organic mobile phases
2014
Column selection in reversed-phase liquid chromatography (RPLC) can become a challenge if the target compounds interact with the silica-based packing. One of such interactions is the attraction of cationic solutes to the free silanols in silica-based columns, which is a slow sorption-desorption interaction process that gives rise to tailed and broad peaks. The effect of silanols is minimised by the addition of a competing agent in the mobile phase, such as the anionic surfactant sodium dodecyl sulphate (SDS). In micellar-organic RPLC, the adsorption of an approximately fixed amount of SDS monomers gives rise to a stable modified stationary phase, with properties remarkably different from th…
Comparative study of solvation parameter models accounting the effects of mobile phase composition in reversed-phase liquid chromatography
2007
Solvation parameter models relate linearly compound properties with five fundamental solute descriptors (excess molar refraction, dipolarity/polarizability, effective hydrogen-bond acidity and basicity, and McGowan volume). These models are widely used, due to the availability of protocols to obtain the descriptors, good performance, and general applicability. Several approaches to predict retention in reversed-phase liquid chromatography (RPLC) as a function of these descriptors and mobile phase composition are compared, assaying the performance with a set of 146 organic compounds of diverse nature, eluted with acetonitrile and methanol. The approaches are classified in two groups: those t…
Performance of a Chromolith RP-18e column for the screening of β-blockers
2009
The chromatographic performance of a monolithic column (Chromolith RP-18e) was comprehensively examined in the isocratic separation of ten beta-blockers, using ACN-water mobile phases, and compared with the performance of three microparticulate RP columns manufactured with different types of silica: Spherisorb ODS-2, Kromasil C18 and XTerra MS C18. The comparison considered the analysis time, selectivity, peak shape (column efficiency and asymmetry) and resolution, and was extended to a wide range of mobile phase compositions. The Chromolith column showed good performance for the analysis of beta-blockers with regard to the packed columns. In terms of selectivity and analysis time, the grea…
Prediction of peak shape in hydro-organic and micellar-organic liquid chromatography as a function of mobile phase composition
2007
A simple model is proposed that relates the parameters describing the peak width with the retention time, which can be easily predicted as a function of mobile phase composition. This allows the further prediction of peak shape with global errors below 5%, using a modified Gaussian model with a parabolic variance. The model is useful in the optimisation of chromatographic resolution to assess an eventual overlapping of close peaks. The dependence of peak shape with mobile phase composition was studied for mobile phases containing acetonitrile in the presence and absence of micellised surfactant (micellar-organic and hydro-organic reversed-phase liquid chromatography, RPLC). In micellar RPLC…
A comparative study of the performance of acetonitrile and methanol in the multi-linear gradient separation of proteic primary amino acids
2006
The performance of the separation of proteic primary amino acids using multi-linear gradients of acetonitrile and methanol was studied under an experimental-design basis, using an Inertsil ODS-3 column and pre-column derivatization with o-phthaldialdehyde (OPA) and N-acetyl-l-cysteine (NAC). Elution strength, peak properties, resolution, and analysis time, were examined. The optimal separation was established through modeling, using information obtained from isocratic data. By optimizing the separation with gradients of increasing complexity, acceptable resolution was possible, being glycine/threonine the critical pair. Multi-criteria decision-making (Derringer desirabilities) was applied t…
Interpretive optimisation strategy applied to the isocratic separation of phenols by reversed-phase liquid chromatography with acetonitrile–water and…
2000
An optimisation protocol is presented for the resolution of complex mixtures in isocratic RPLC with binary mobile phases of organic solvent and water, which is based on the prediction of peak position and shape of the individual compounds. A good description of the retention was achieved through the application of statistical weights to the widely used linear or quadratic relationships between the logarithm of the retention factor (log k) and the organic solvent concentration in the mobile phase. The maximisation of the product of peak purities for each compound is shown as a competitive resolution strategy versus the worst value of a selectivity parameter. Peak purities allow one to associ…
Optimised procedures for the reversed-phase liquid chromatographic analysis of formulations containing tricyclic antidepressants.
2003
The chromatographic behaviour (retention, selectivity, peak shape and resolution) of seven tricyclic antidepressants (TCAs), amitryptiline, clomipramine, doxepin, imipramine, maprotiline, nortryptiline and trimipramine, was examined. Conventional unendcapped Cs and C18 columns and an endcapped XTerra MS C18 column recommended for the analysis of basic compounds were used together with acetonitrile-water and micellar sodium dodecylsulfate (SDS)-pentanol mobile phases. The two best combinations were XTerra C18/acetonitrile, which yielded the largest efficiencies and resolution, and C8/SDS-pentanol, which eliminated the peak tails that were still observed with the XTerra C18 column. Both the s…